The present invention relates to a bottom structure of a biaxially-oriented blow-molded bottle-shaped container made of a synthetic resin such as polyethylene terephthalate or the like, which bottom structure has high mechanical strength such as impact resistance and stably exerts good “seat” function.
In a general structure of a self-standable bottom of a biaxially-oriented blow-molded bottle-shaped container made of a synthetic resin, particularly polyethylene terephthalate, a bottom wall is constructed in a domed shape, wherein a lower edge of said bottom wall and a lower edge of a container body are connected with a ground wall of in convex state downwardly, and said ground wall functions as a leg, so that the bottle-shaped container is self-standable.
Since the above described bottle-shaped container is formed by biaxially-oriented blow-molding, an orientation magnification at the ground wall that functions as the leg for the bottom is large. Hence, there is a disadvantage that a thickness of the wall at the ground wall tends to be thin. In particular, in case of a large bottle-shaped container with a content of 2 liters or more, such thin wall at the ground wall may be cause insufficient mechanical strength and unsteady “seat” function of the bottle-shaped container.
Particularly, in recent time, due to strong requirement of minimization of resource consumption, the thickness of a bottle-shaped container of the above-described type tends to be thinner. Hence, there is a strong tendency such that the thickness at the ground wall tends to be further thin. Hence, the above-described disadvantage occurs remarkably and more easily.
In order to resolve the above-described disadvantage, JP-A-H09-510168 (derived from WO-A1-95-25041, particularly, claims, FIG. 2 and FIG. 4) discloses a bottle-shaped container comprising a neck designed so as to adapt to receive a cap, a substantially cylindrical side wall, and a bottom, wherein said bottom has a concaved or hollowed central portion and a convex circumferential surface wall, said convex circumferential surface wall includes radially-arranged grooves and connects to the concave central portion in the bottom via a substantially flat annular surface, and each of the radially-arranged grooves at a bottom thereof and the flat annual surface are substantially in contact and connected with each other.
Further, JP-A-H05-254532 discloses a bottle circumferentially formed with a plurality of bottom-reinforcing sections comprising concave and/or convex portions in a proximity of a lower end of a wall of a bottom.
In said JP-A-H09-510168, however, a thickness of the circumferential surface wall is thin, because the blow ratio of the circumferential wall that forms legs is high. Therefore, the grooves can reinforce the circumferential surface only near the grooves. Hence, there is a problem that a number of grooves are required to be provided, whereby a structure of the bottom becomes complex, and that differences in thicknesses between the groove portions and the circumferential surface wall portions occur consequentially, so that said differences cause the thickness of the circumferential surface further thin.
In said JP-A-H05-254532, since said bottom-reinforcing sections are provided in the circumferential wall portion (that is, a heel portion of the bottle, where the bottom is connected to the body), only the heel portion is reinforced in the bottom. A portion exerting grounding function is not reinforced at all. Hence, there is a problem in the past that stable “seat” function cannot be obtained by JP-A-H05-254532.